KR20030058098A - Method for controlling beam pattern in mobile communication using smart antenna - Google Patents

Abstract

PURPOSE: A beam pattern control method in a mobile communication system using a smart antenna is provided to increase a capacity of a forward link of a base station and enhance a communication quality by accurately estimating a direction or a terminal by the base station. CONSTITUTION: Position information of a terminal and a resolution of the information are fed back to a base station through a reverse control channel. The base station analyzes the position information and ACK and NACK information for a forward packet and performs a transmission to an entire sector, or forms a beam pattern of a specific direction to transmit a signal. The base station informs whether to use a common pilot or an auxiliary pilot in the next frame through a forward control channel. The base station transfers data by using the determined beam pattern. In a packet data channel of 1xEV-DO system, the frame is replaced with a slot. That is, the base station selects a pilot by the unit of slot, and the terminal buffers the pilot and data to search a phase of the pilot, and starts demodulation.

Description

Method for controlling beam pattern in mobile communication system using smart antenna

The present invention relates to beam pattern control in a mobile communication system using a smart antenna, and more particularly, to a beam pattern control method in a mobile communication system using a smart antenna capable of providing an effective beam pattern in a forward direction in a multi-user and multipath environment. It is about.

In order to provide high speed data communication to multiple subscribers in a mobile communication system, it is important to increase the capacity of a cell.

Basically, since mobile communication such as cellular and PCS starts from the basic concept of effectively using a limited spectrum, dividing the cells more and more increases the efficiency of the spectrum. However, the method of splitting a cell has a disadvantage in that a large amount of additional costs are required to install a base station as well as a communication failure due to frequent handoff or a decrease in communication reliability.

In particular, as the demand for high-speed data communication increases in the next generation mobile communication system, throughput per sector of the base station becomes an important concept. In particular, the forward channel may require very high cell capacity due to data download requests of terminals. To this end, a method of using a smart antenna is currently being actively studied.

Therefore, recently, new researches are being conducted that can significantly increase communication capacity and improve communication quality by applying advanced antenna technology without increasing base stations.

One of them is using smart antenna technology to concentrate radio waves in the direction of the desired subscribers, reduce the interference signal of other subscribers and transmit and receive the technology to significantly improve the performance of the existing mobile communication system.

Smart antenna technology is a state-of-the-art beamforming technology implemented by using a combination of an antenna array and a digital signal processing technology that can control the propagation direction has attracted great interest among carriers.

That is, in general, a base station antenna of a mobile communication system is manufactured to give a constant gain regardless of a direction by using an omni-directional antenna.

In this case, all signals transmitted / received to the antenna are transmitted and received by controlling power according to the distance from the base station's transmit / receive antenna and affect the desired signal. Therefore, this base station antenna selectively gains and cannot transmit and receive a signal.

In order to reduce the effects of such interference, there is a method of dividing a cell into several sectors and using multiple antennas. For example, if a cell is divided into three sectors and three antennas are used to make each antenna cover 120 degrees, the effect of the interference may be reduced. It can be reduced to 1/3.

Another way to reduce the effects of interference is to have the antennas fixed in hardware, so that the antennas have a large gain for signals arriving from a given angle and very small gains for interference signals transmitted and received in different directions. However, this method should be limited to the case where the transceiver is fixed.

A more advanced method is to use an array composed of several antenna elements when the transmitter transmitting the desired signal moves or the angle of arrival of the signal varies depending on the situation.

Antenna arrays are used to locate remote signal sources or to selectively transmit and receive signals from them and to remove interference from the surroundings.

In the case of using such a smart antenna system, the interference between subscribers can be greatly attenuated by selectively transmitting and receiving a signal in a desired direction and minimizing the influence of the interference signal. That is, the amount of propagation can be minimized in other terminal directions by providing independent beams to each terminal in the cell between transmission and reception, and by forming a beam to maximize them in a desired terminal direction. Therefore, the noise of the received signal is greatly attenuated.

The smart antenna system is a system that can improve the call quality and increase the number of subscribers by minimizing the interfering noise between call channels.The battery life is also dramatically reduced because the radio waves are concentrated in the desired direction so that each terminal can talk at low power. It is a technology that can be extended. As a result, the smart antenna system can increase the communication capacity and significantly improve the communication quality by providing an independent beam pattern toward each terminal.

As a result, by providing a directional beam pattern to all subscribers in the cell, it sets the maximum gain in the call direction and minimizes the gain in the other directions. It is provided in both transmit and receive directions and simultaneously simultaneously to all subscribers in the cell. Such an optimal beamforming technique should install an array antenna at the base station and independently calculate the optimal weight for each subscriber and provide it to each subscriber.

In the CDMA environment, the desired signal and the interference signal are separated by the PN code. By using this principle, by calculating the unique vector value received for each subscriber and adjusting the array antenna phase, the arrayed antenna forms an independent beam pattern in the direction of the signal source. That is, the m beamforming modules can independently phase-array n array antennas, which form a beam pattern toward each subscriber to improve call quality by maintaining a large signal difference between a desired signal and an interference signal.

However, the conventional smart antenna algorithm can greatly increase the system capacity of the reverse link, but there are some difficulties in increasing the capacity of the forward link.

For example, in the frequency division duplexing (FDD) system, since the frequency of the forward channel and the reverse channel is different, the propagation characteristics are different. In such a case, applying the beam pattern obtained through the reverse channel to the forward direction is the worst case. Inadvertently lowering cell capacity.

This is because the beam pattern control of the forward channel is extracted from the array antenna control information by the reverse channel and used as it is. In particular, in a multi-path mobile communication environment, it is dangerous to apply the antenna control information obtained from the reverse channel to the forward channel as it is, and research on beam pattern control in the forward channel is currently in progress.

The present invention has been made to solve the problems of the prior art described above, the base station can perform the control of the beam pattern in the forward channel by estimating the direction of the terminal according to the location information of the terminal transmitted through the reverse channel It is to provide a beam pattern control method in a mobile communication system using a smart antenna.

In the method of controlling a beam pattern in a mobile communication system using the smart antenna of the present invention, the terminal transmits its location information to a base station through a reverse channel, and the base station determines the direction of the terminal according to the location information. The method may include: analyzing, by the base station, the quality of the forward channel with respect to the direction of the terminal, and determining a forward beam pattern formation direction for the terminal according to the analysis result.

Preferably, the location information includes its own location information analyzed by the terminal according to the satellite positioning system service and reliability information about the analyzed location information.

The analyzing of the quality of the forward channel may include forwarding forward packets from the base station to the user equipment and, if there are many acknowledgment signals according to the presence or absence of an acknowledgment (ACK) signal of the user equipment that has received the forward packets, the quality of the forward channel may be increased. It is evaluated as excellent.

Preferably, the determining of the direction of forming the forward beam pattern for the terminal determines that the gain value of the forward beam pattern is concentrated in the direction of the terminal when it is determined whether the quality analysis result of the forward channel is superior to a set threshold value. If it is not better than the threshold value, the forward beam pattern is determined to be omni-directional of the base station sector, and determining the direction of the forward beam pattern formation direction for the terminal is set in the base station the distance of the terminal and the base station If it is determined that the value obtained by dividing the accuracy of a beam pattern angular rate by the location information accuracy of the terminal is superior to the accuracy threshold of the beam pattern, the forward beam pattern is determined to be concentrated in the direction of the terminal, and is superior to the threshold. If it is not determined that the omni-directional of the base station sector Decide if possible.

1 is a view for explaining a method for extracting the DOA and the distance from the location information of the terminal and the base station according to the present invention;

2 is a diagram illustrating a beam pattern control scenario between a terminal and a base station for explaining a beam pattern control method according to the present invention;

Hereinafter, a beam pattern control method in a mobile communication system using a smart antenna according to the present invention will be described with reference to the accompanying drawings.

1 is a view for explaining a method for extracting the direction and distance of the terminal from the location information of the terminal and the base station according to the present invention, Figure 2 is a view between the terminal and the base station for explaining the beam pattern control method according to the present invention A diagram illustrating a beam pattern control scenario.

For beam pattern control on the forward channel, information about a direction of angle (DOA) is important. Currently, many algorithms for calculating the direction of a terminal based on reception information through an array antenna have been proposed. However, in a mobile communication environment in which multiuser and multipath are severe, The forecast is very uncertain.

Therefore, in the present invention, the smart antenna system is used as it is to increase the capacity of the reverse channel, but in the case of the forward channel, in the method of controlling the beam pattern by receiving feedback of the position information of the terminal from the reverse channel, confirming the position of the terminal Use service that can be.

As a service capable of confirming the location of such a terminal, an E-911 (Enhanced-911) service, which is recently requested in the United States, is used. Currently, in the United States, the terminal user's location accuracy within 150m to prepare for emergencies of the terminal user.

In this case, the location information of the terminal user is determined using, for example, a global positioning system (GPS).

Here's a brief description of GPS: GPS was created for military purposes to measure the position of objects on Earth and is now used by civilians. Using GPS, location and time can be obtained. GPS positioning data is within 50 m for the Precision Positioning Service (PPS) used for military purposes, and within 200 m for the Standard Positioning Service (SPS) provided to the civilian. Has an error range of. As a method of correcting such an error, differential GPS (DGPS) reflecting data corrected by using a difference between a coordinate value of a specific position and a measured value therein is used. Using DGPS, the margin of error can be reduced to within 5 m. Recently, DARC system, which provides DGPS correction data through FM broadcasting, is also introduced in Korea. Initially, GPS was used in conjunction with electronic maps (GIS) for airplanes, ships, and vehicles, but recently, it is also used to locate people such as people and vehicles. In addition, personal portable GPS receivers have been developed and used for unknown exploration and self positioning during military operations. Recently, a GPS receiver in a portable cordless phone has been developed and released.

Therefore, using the US E-911 or GPS can be used to determine the direction of the terminal (DOA) because the location of the terminal can be known within 50m range.

First, as shown in FIG. 1, the terminal calculates its position. In this case, in the case of E-911, the accuracy (resolution) is set to 150 m or less, but in reality, the position of the terminal can be calculated with accuracy of 50 m or less.

The terminal periodically feeds back the calculated position information together with the accuracy of the information and reliability information about the position information to the base station. The feedback period may be in the order of tens to hundreds of milli-seconds.

This information is transmitted to the base station via the reverse control channel.

Since the base station knows exactly its location, the base station can calculate the direction of the terminal (DOA) together with the distance from the base station to the terminal using the transmitted feedback information.

If the feedback information about the current position is not reliable, the previous reason information is used but the accuracy is slightly reduced (coarse resolution).

The base station controls the beam pattern to the terminal by using the direction (DOA) information of a given terminal. And if the terminal is close to the base station (BS) because of the margin (margin) for the accuracy of the position it is not possible to estimate the correct direction. In this case, since the base station can transmit the entire sector with low power, it does not significantly deteriorate the capacity of the entire system. If the unreliable information is continuously fed back, the accuracy of the location information continues to fall, and thus the direction of the terminal (DOA) information becomes useless. In such a case, an existing omni-directional antenna or sectorized antenna is used as it is.

After using the directional beam, even if the NACK for the frame is greatly increased from the terminal, the existing omni-directional antenna or sectorized antenna is used as it is.

In this case, if the existing transmit diversity gain is to be obtained, the base station should have the transmit diversity antenna in addition to the array antenna.

Parameters for determining the direction of the terminal (DOA) in the present invention, the determination method and the conditions for using the directional beam are shown in the table.

Parameter Range Accuracy Quality (PR) 50m, 100m, 150m, unreliable Distance from base station (D) Meters Beam Width Resolution (BWR) Angle ratio of beam width (preset at base station) (Degree of angle) FL frame ACK, NACK history

In the case of using beamforming, a variable called FL_Quality (forward link quality) is continuously updated using the results of ACK and NACK to evaluate the quality of the forward channel for each terminal.

One method may be to decrease the FL_Quality value by an appropriately small step when an ACK comes in, and to increase the FL_Quality value by an appropriately large step when a NACK is transmitted.

Therefore, when FL_Quality is equal to or greater than a certain threshold FL_Quality_Thresh, it is determined that there is a problem in the current beam forming, and the narrow beam forming is not performed for a predetermined time in the future. As a result, the present invention proposes the following two conditions as conditions for using narrow beam formation.

The first condition is FL_Quality <FL_Quality_Thresh,

The second condition is D × BWR / PR〉 Beam_Res_Threshold.

The Beam_Res_Threshold is a threshold value for determining whether the direction of the terminal (DOA) can be used by the beam width when using the array antenna from the position information of the current terminal and the accuracy of the position.

In summary, the control of the reception beam pattern for the reverse channel always uses an adaptive array method, and the reception beam control for the forward channel will be described with reference to FIG. 2 as follows.

The position information of the terminal and the resolution of the information are fed back to the base station through the reverse control channel (S11).

The base station analyzes the location information and the ACK and NACK information for the forward packet to transmit the entire sector or forms a specific direction (DOA) beam pattern to transmit a signal.

Whether to use a common pilot or auxiliary pilot in the next frame through the forward control channel (notices when a change occurs) (S12).

Subsequently, data is transmitted using the determined beam pattern (S13).

For the packet data channel of the 1xEVDO system, the concept of the above frame is mapped to a slot. That is, the base station selects a pilot in each slot unit (Common 0r auxiliary), and the terminal buffers the pilot and data to find the pilot phase and starts demodulation (in the case of a common pilot, buffering is not necessary).

In the cellular system, the control of the beam pattern using the array antenna at the base station can greatly increase the capacity of the cell. However, in determining the beam pattern for the forward channel, the beam pattern obtained to optimize reception of the reverse channel is used as it is. When used, the effect will be greatly reduced, especially in a mobile communication environment with strong multi-user and multi-path characteristics. That is, it is possible to reduce the number of systems by inaccurately controlling the beam pattern for the forward channel. In the present invention, in determining the beam pattern for the forward channel, the direction of the terminal (DOA) calculated from the position of the terminal is used. This makes it possible to perform beam pattern control on the forward channel much more stably.

In the beam pattern control method of the mobile communication system using the smart antenna of the present invention, since the base station can accurately know the direction of the terminal according to the position information transmitted from the terminal, the effective beam pattern control in the forward direction is possible. Increasing the capacity has the effect of improving the communication quality, especially in high-speed data communication.

Claims (5)

Transmitting, by the terminal, its location information to the base station through a reverse channel; Determining, by the base station, the direction of the terminal according to the location information; Analyzing, by the base station, quality of a forward channel with respect to a direction of the terminal; And determining a direction of forming a forward beam pattern for the terminal according to the analysis result. According to claim 1, wherein the location information is a mobile communication system using a smart antenna, characterized in that the terminal analyzes its own location information and the reliability information about the analyzed location information according to the satellite positioning system service Beam pattern control method The method of claim 1, wherein the analyzing of the quality of the forward channel comprises: transmitting a plurality of forward packets from the base station to the user equipment and receiving a large number of acknowledgment signals according to the presence or absence of an acknowledgment (ACK) signal of the user equipment that has received the forward packets. Beam pattern control method in a mobile communication system using a smart antenna, characterized in that the quality of the forward channel is evaluated as excellent. The method of claim 1, wherein the determining of the forward beam pattern formation direction for the terminal comprises: concentrating the gain value of the forward beam pattern in the direction of the terminal when it is determined whether the quality analysis result of the forward channel is superior to a predetermined threshold value. And determining that the forward beam pattern is omni-directional of the base station sector if it is not superior to the threshold value. The method of claim 1, wherein the determining of the direction of the forward beam pattern formation direction for the terminal comprises: a value obtained by dividing the accuracy of the distance between the terminal and the beam pattern angle ratio set by the base station by the position information accuracy of the terminal; If it is determined that it is superior to the accuracy threshold of the beam pattern, it is determined that the forward beam pattern is concentrated in the direction of the terminal, and if it is not determined to be superior to the threshold value, it is determined to be omni-directional of the base station sector. Beam pattern control method in a mobile communication system using a smart antenna.